Perhaps no human activity, other than killing other humans, has a longer history than diet regulations that prohibit some foods and glorify others. Even in the biblical garden of paradise there was forbidden fruit. And the reasoning behind forbidden fruit is always the same. Eating the right foods and avoiding the wrong ones means living longer, perhaps forever. Humans are always suckers for that pitch.
Just as the prohibition against meat on Fridays in the Catholic Church helped the fishing industry in medieval Italy, so the latest fad, the Paleo diet, should prove to be a boon to grass-fed chicken and livestock producers because Paleos are supposed to eat only meat raised on grazed pastures without, heaven forbid, grains. The Paleo philosophy believes that modern meats no longer have the nutritional value of the wild meat that prehistoric humans enjoyed. Modern meat has turned real, red blooded cavemen and cavewomen into pansies. Today the only easily obtainable meat that comes close to the wild meat of Paleolithic times is the grass-fed kind.